This invention is directed to a method of making an improved cellular spacer-support structure for luminescent display panels and the like. The invention is known to have utility when used in the manufacture of flat display panels of the gas-discharge type, and especially gas-discharge display panels of the cellular type in which individual display elements, or groups of elements, are formed in discrete cells.
It is conventional in prior art gas-discharge display panels of the cellular type to have an envelope including hermetically sealed front and rear glass slabs. A regular array of gas-discharge cells is established within the envelope at the locations of the intersections of orthogonally arranged row-selection and column-selection electrodes. Gas discharges are selectively established at the intersections of excited pairs of row-selection and column-selection electrodes.
It is common to provide other electrodes for discharge ignition, for current modulation, for scanning the discharge, etc. In certain panels such as disclosed in U.S. Pat. No. 3,845,241, each gas discharge is coupled to a cathodoluminescent stage. Electrons are extracted from the gas discharge and accelerated in the cathodoluminescent stage to excite a phosphor on the inner surface of the viewing window.
The various types of gas-discharge panels, and display panels in general, require one, and in some cases a series, of insulative spacers for separating the various arrays of electrodes within the panel enclosure. It is also common in the prior art to impose on the insulative spacer structure the added function of providing mechanical support against the atmospheric pressure exerted on the extended surfaces of the evacuated panel enclosure. Gas-discharge panels of various types having insulative spacers which appear to also provide structural support are disclosed, for example, in U.S. Pat. Nos. 3,921,021; 3,938,135; 3,798,483; 3,803,439; and 3,753,041.
The constraints imposed upon such insulative spacer-support structures are manifold and challenging. Two obvious requirements are that the structure be electrically insulative and capable of withstanding high compressive forces. Regarding the latter constraint, simple calculations will show that for a flat panel having, for example, a 30-inch diagonal measurement, several tons of atmospheric force are exerted on the face of the panel.
Another requirement imposed upon such spacer-support structures in many panel applications is that the cell passageways by relatively deep, compared to their smallest lateral dimension. For example, the passageways in some applications necessarily must each have a front-to-back depth which is many times its narrowest width dimension.
Further, it is desirable that the passageways be capable of being formed to very small lateral dimensions and be capable of being precisely located in order that high-resolution displays may be made. The spacer-support must be capable of withstanding thermal cycling and other operations to which the panel is subjected during its fabrication and assembly, without intolerable degradation in accuracy of dimensions of the overall structure of the passageways formed therein.
It is very important that the spacer-support structure be capable of manufacture at acceptably low cost. Desirably, the structure should be capable of being easily modified or tailored for added functions or unique applications. In some panel applications, it is desirable that the spacer-support facilitate conditioning of adjacent cells by permitting migration of ions and metastables to adjacent cells to condition them for ready ignition when selected.
Various approaches to fabricating insulative cellular spacer-support structures have been explored. Perhaps the most common method employed for fabricating such structures is by the use of photo-etching techniques. Such an approach is disclosed in such prior art U.S. Pat. Nos. as 3,953,756; 3,789,470; and 3,777,206. One of the problems attending the use of certain etching methods is that the etched material is rapidly "undercut". The implication of this is (see U.S. Pat. No. 3,777,206) that if passageways are to be formed which are relatively deep compared to their lateral dimensions, then such a structure must be built up as a stacked plurality of mutually registered, separately etched layers. Inadequate dimensional accuracy and high cost also plague certain other etching methods.
An alternative approach, disclosed in U.S. Pat. No. 3,885,195 is to use a plurality of parallel glass ribs, shown as being trapezoidal in cross-sectional configuration, which are placed between front and rear slabs of a panel in order to provide the necessary insulation, support and spacing functions.
U.S. Pat. No. 3,953,756 suggests that an insulative spacer-support can be formed by machining a suitable material. U.S. Pat. No. 3,843,427 suggests that a spacer-support structure can be cast. Still another approach is disclosed in U.S. Pat. No. 3,611,019. U.S. Pat. No. 3,611,019 shows a hollow, thin-walled glass box-like structure containing an interwoven single layer mesh of insulative fibers which support the thin walls of the structure. In U.S. Pat. No. 3,611,019, the spacer-support also serves to contain the ionizable gas, excitation of which is achieved through the thin walls of the structure by orthogonally arranged electrodes disposed in contact with the opposite walls of the structure.
None of the prior art spacer-support structures have been found to be completely satisfactory. Most, if not all, have severe limitations in terms of their cost. Most of the prior art approaches are deficient in their ability to produce spacer-support structures having passageways whose individual depth is greater than its smallest lateral dimensions. Certain of these prior art approaches cannot meet the degree of accuracy in placement and configuration of the passageways which is required; other approaches fail when subjected to the severe thermal cycling operations which a panel must undergo during its fabrication. In short, there exists in the art prior to this invention a very strong need for an improved spacer-support structure for luminescent display panels.
This invention is directed to a method of making a spacer-support structure which comprises a stack of mutually registered lattices of filaments adhered together to form a structure defining an array of passageways therein. In this connection, reference is had to U.S. Pat. No. 3,829,734--Schofield. The Schofield patent does not concern the provision of a spacer-support structure or a method of making same, but rather discloses a technique for interweaving a fabric of glass fibers into a mesh of crossed column and row electrodes. The fibers act to space the electrodes and to capture the crossed electrode structure in a unitary fabric. The Schofield patent discloses merely an improvement on an earlier-known technique of interweaving crossed electrodes into a simple mesh (see U.S. Pat. No. 3,602,756--Bonnet), which earlier technique does not employ glass fibers to space the cross electrodes.